Changing worn-out disc brake pads is a straightforward job. The best way to tell if they need replacing is a visual inspection. Some pads have a groove that serves as a wear indicator; if not, look through the caliper to see if the pad looks thin. Otherwise, some cars have a warning light to let you know if the pads are nearly worn down to the rivets, while others have brakes with a strip of metal that starts to squeal against the rotor when the pads are worn way down.

When it's time to change the pads, make sure you have jack stands, basic hand tools, and a C-clamp (to push the caliper piston into its cylinder) on hand. If badly worn pads have severely scored the rotor, this would also be the logical time to replace that; it slips off the hubs once the caliper and its bracket are removed.

Novice mechanics can change their headlight bulbs but accessing the bulbs can be complicated. Once you've opened the hood, see if the three-wire plug at the back of the headlight assembly is visible. If not, you'll have to jack up that side of the vehicle, remove the wheel, and see what's necessary to loosen the fender panel. (The panel is held in place with fasteners that are unique to each car model.) Once you can reach the headlight plug, remove it by unfastening the clip, screw cap, or plastic catch that holds it in place, and pull out the bulb. After you pull out the bad bulb, be sure to hold the replacement bulb by its plastic housing. Don't touch the glass, not even with latex gloves.

That Check Engine light might also come on if you have a faulty exhaust-gas-recirculation (EGR) valve. EGR valves are pollution-control devices that reduce nitrogen-oxide emissions by sending a little exhaust gas into the intake manifold. If your EGR valve is faulty, you'll notice rough idling, engine knocking, poor fuel consumption, overheating, or even a failed emissions test. Once you've found the EGR valve (usually at the back of the engine bay on the driver's side), disconnect the electrical and vacuum lines leading into it and unscrew the valve with a socket wrench. That's all you have to do before installing the replacement valve.

If you hear or feel some thumping around your feet as you drive your vehicle, the source could be worn-out bushings on either side of the front antiroll bar. Replacing those bushings is not always easy or straightforward because, among other hurdles, there could be chassis components blocking them. But if the bushings are easily accessible, the job is doable for a weekend DIYer.

First, secure the front of the car on jack stands. Then locate the sway bar, which spans the width of the chassis and links the front suspension assemblies. Replacing the bushings is as simple as unfastening each of the single bolts that attach the sway bar to the lower suspension arms. Note: If you've been hearing a squeak instead of a knocking, it's probably the ball joints, and replacing those is definitely not for novices.

In most cars, a warning light will tell you when the alternator is dying. If not, you'll know soon enough when your car stalls (from running off a depleted battery) or won't turn over when you try to start it. Novice mechanics can replace dead or dying alternators as long as the alternators are accessible from the top of the engine. (If they're down around the bottom of the block, they can be impossible to see and you have to work by feel to get them out and replace them; that takes experience.)

To do the job, you'll need wrenches, including a socket wrench. Some cars might also require a special tool to take the tension off the belt. And be sure to do things in the proper order. Unbolting the alternator before detensioning the belt could cause both of them to bind up so that you won't be able to budge either of them.

The fluid in your automatic transmission will degrade significantly if it's exposed to very high operating temperatures. To be absolutely sure your automatic transmission is properly lubricated, the fluid should be changed at the intervals specified in the manual (usually every 15,000 to 30,000 miles).

If you decide to follow that maintenance schedule, you should also change the transmission filter. Secure the car on four jack stands, empty the fluid through the drain plug (if your car has one), then unbolt the pan. If you don't have a plug you'll need to slowly remove the bolts, leaving the forward-most bolts attached, but loose, so the pan can tilt down to drain (and you'll want a large drip pan). Once it's off, the filter is easily seen and replaced. After reattaching the pan, refill the transmission through the dipstick tube, which you'll find in the engine bay. Use a long-nose funnel intended for transmissions, and pour in the recommended volume of fluid.

Then start the engine, let it run until it reaches normal operating temperature, shift through the gears while stopped, and check the fluid level while in park. Add more fluid as needed, being careful not to overfill. And be sure you're using exactly the fluid grade specified in the owner's manual. Using the wrong fluid can seriously damage your transmission.

If your engine is overheating or is slow to warm up, your thermostat could be either stuck shut or stuck open. Replacing the thermostat can be a straightforward job that won't require draining all of the engine coolant. In the vast majority of cars, you'll find the thermostat where the top radiator hose goes into the engine.

Look for two or three bolts holding the thermostat housing in place beside the entry point. Before detaching the radiator hose so you can put a wrench on the bolts, place a pan or bucket below the engine—you're likely to spill some coolant. After unbolting the old thermostat, check to ensure that the replacement gasket is a perfect match for the old one. One more thing: On some of the older cars you could put the thermostat in upside down. Nowadays, most of them have designs that prevent them from going in upside-down.

If your sunroof is leaking for reasons other than a crack in the glass, the problem is probably plugged drain holes. Open up the sunroof and clean any debris in the tracks.

Then find the drains, which are usually in the corners. If you don't have an air compressor and a "wand" for the air-compressor hose, you might try going to your local convenience store and using their compressed air to shoot blasts into the drains to clear them. You could also try unclogging the drains with a section of wire coat hanger. Just be gentle when you push the wire into the drain line.

A common problem that trips the Check Engine light on your dashboard is a faulty oxygen sensor. This is one of the many times you'll need an OBD II scan tool, at least if your car is a 1996 or newer model year. If the scan tool points to an O2 sensor, be aware that vehicles can have as many as four O2 sensors in the exhaust system—one or two before the catalytic convertor and one or two after.

They look like spark plugs, and your diagnostic tool might be able to tell you which one needs replacing. (If not, you'll need someone with a higher-tech scanner to identify it.) The O2 sensor can be removed with an open-end wrench, but you should buy a socket specifically designed for the sensors from your parts dealer because it will have a groove for that outgoing wire. Spray some penetrating oil on the base of the sensor before attempting to turn it with a wrench; it'll make the job easier.

If your car is idling poorly and stalls when you put it into gear, you could have a faulty idle-air-control valve or a faulty sensor. (You'll have a Check Engine light glowing, too.)

If your OBD II scan tool identifies the sensor as the problem, simply follow the hose leading out of the air cleaner to the throttle body, which is on top of the engine; it controls the flow of air into the fuel-injection system. Replacing the sensor requires only removing a pair of screws. If the diagnosis indicates that the valve itself is faulty, you're still in business: the valve is also held in place with just a pair of screws.